This application claims benefit of priority under 35USC xc2xa7 119 to Japanese Patent Application No. 2001-27197 filed on Feb. 2, 2001 in Japan, the entire contents of which are incorporated by reference herein.
The present invention relates generally to a semiconductor light detecting device, and more particularly to a semiconductor light detecting device enabling a high-speed response in a way that keeps a light detection sensitivity in applications to optical communications and so on.
The semiconductor light detecting device is broadly used in applications to the optical communications, a variety of optical monitors and others. Purposes for converting the light into electric signals in these applications are to detect a light intensity and modulated light, observe a waveform of an optical pulse, and convert an energy as by a solar battery. Basic characteristics required of the semiconductor light detecting device are that a photoelectric conversion efficiency be high in a wavelength band of the light to be detected, that there be a response speed required, and that noises be low. Further, the semiconductor light detecting device needs to be small both in size and in weight, and low both in its operating voltage and in its price in the majority of cases.
Responding to these demands, a semiconductor light emitting device based on a pn junction diode is used. A scheme of this semiconductor light emitting device is that a backward bias is applied to the pn junction provided in the semiconductor, and photo carriers generated by a light absorption in a depletion layer therein are detected as a photoelectric current.
Over the recent years, the semiconductor light detecting device has been required to have a high-speed response characteristic of which a cut-off frequency is equal to or higher than 10 GHz in the various categories of applications such as the optical communications and so forth.
A conventional pn junction diode type semiconductor light detecting device has a problem in which the response speed of the device is hard to gain a remarkable improvement.
According to one embodiment of the present invention, there is provided a semiconductor light detecting device comprising:
a light absorbing layer; and
a pn junction, carriers generated by said light absorbing layer absorbing the light in a light detecting region being detected as a photoelectric current through a depletion layer provided by applying a backward voltage to said pn junction,
wherein said light detecting region in said light absorbing layer is all depleted in a state where an operating voltage is applied.